A woman cries during the funeral of a man who was killed in BanguiReuters

The international war crimes prosecutor has opened an investigation into potential war crimes or crimes against humanity in the Central African Republic.

The prosectur, Fatou Bensouda, said that the situation for civilians in the country has "gone from bad to worse" since September 2012, and she has recently received reports of "extreme brutality by various groups."

Thousands of Muslim fled their homes in Bangui on Friday. One man who fell off a truck was subsequently killed and his body mutilated.

Several trucks broke down before they could leave Bangui on Friday and had to be abandoned. The passengers jumped aboard other trucks, facing constant jeering, threats and stone throwing from the watching crowd.

"The Christians say the Muslims must go back where they came from, that's why we are going home," said Osmani Benui as she fled Bangui.

"We had no possibility to stay on because we had no protection."

In recent weeks, angry mobs have set fire to mosques and killed and mutilated Muslims.

A man was killed in a mob lynching on Wednesday just minutes after President Catherine Samba-Panza had outlined plans at a public rally in Bangui to rebuild the national army to take over security from international peacekeepers.

Sixteen hundred French and 4,000 African troops are in CAR trying to end the fighting.

Muslim communities in many towns in the CAR are threatened from reprisal attacks on civilians, Medecins Sans Frontieres (MSF) warned.

"Civilians remain in constant fear for their lives, and have been largely left to fend for themselves," Martine Flokstra, MSF's emergency co-ordinator, said in a statement.

"We are concerned about the fate of these communities trapped in their villages, surrounded by anti-Balaka groups, and also about the fact that many Muslim families are being forced into exile to survive," Flokstra continued.

Amnesty International has highlighted crimes against humanity being committed by both warring sides including extrajudicial executions, mutilation and rape.

The conflict, which started in December, has pitted Muslim Seleka forces against Christian Anti-Balaka militias who have engaged in a tit-for-tat violence that has resulted in over 1,000 deaths and left nearly a million people (20% of the population) displaced.